Depending on the use or the power capacity of the battery, the secondary batteries may be classified into lower-power batteries (hereinafter “small battery”) in which one to several battery cells are made into a battery pack, and bulk-size batteries for driving motors (hereinafter “large battery”) in which several to tens of battery cells are connected to form a pack.
Small batteries are used as the power source for various portable electronic devices such as cellular phones, laptop computers, and camcorders. Large batteries can be suitable for the power source of motor driven devices such as the hybrid electric vehicles, wireless vacuum cleaners, motorbikes, or motor scooters.
Generally, small batteries have square and cylindrical shapes, when they are made of one cell. The small battery includes an electrode assembly in which a separator as an insulator is interposed between a positive plate and a negative plate, which are spiral-wound together. The electrode assembly is inserted inside a cylindrical container to form the battery.
A conductive tab, which plays a role in collecting the current produced when the battery is operated, is attached to the positive and negative electrodes. The conductive tab is attached to the electrode assembly by welding, etc., and induces the current produced from the positive and negative electrodes to respective positive and negative terminals.
In the case that the above structure of the small battery is applied to the large battery, the dynamic kinetics necessary for large batteries are not satisfied in terms of capacity and power. Accordingly, there have been provided secondary batteries including a multi-tab structure in which plural tabs are attached to the electrode assembly. Furthermore, there have been provided secondary batteries including a lead element of a plate shape in which a plate is used as the lead element.
The secondary battery with the above structure may have a cylindrical or a hexahedral shape, such as a square-type battery. Plural secondary batteries (e.g. 40 batteries) are made into a battery module.
The dynamic kinetics of the secondary battery for a battery module requiring high power and bulk size require not only a high energy density per unit volume for each of the secondary batteries but also consideration for the battery module's current collecting capacity.